Methods and arrangements for determining the position of an occupant in a vehicle

ABSTRACT

Arrangements and method for determining the position of an occupant of a vehicle situated on a seat in the vehicle in which the position of the seat or a part thereof, e.g., the seat portion or back portion, is determined relative to a fixed point of reference to thereby enable an approximation of the position of the occupant to be obtained. The payout of a seatbelt from a seatbelt retractor can be measured and used to better provide the actual position of the occupant. An additional approximation of the position of the occupant can be obtained by receiving waves from the space above the seat in order to improve the determination of the likely, actual position of the occupant. Once the position of the occupant is determined, it can be used in the control of a deployable occupant restraint device such as an airbag.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/905,877 filed Aug. 4, 1997 which in turn is a continuationof U.S. patent application Ser. No. 08/505,036 filed Jul. 25, 1995, nowU.S. Pat. No. 5,653,462, which in turn is a continuation of U.S. patentapplication Ser. No. 08/040,978 filed Mar. 31, 1993, now abandoned,which in turn is a continuation-in-part of application Ser. No.07/878,571 filed May 5, 1992, now abandoned.

BACKGROUND OF THE INVENTION

Crash sensors for determining that a vehicle is in a crash of sufficientmagnitude as to require the deployment of an inflatable restraintsystem, or airbag, are either mounted in a portion of the front of thevehicle which has crushed by the time that sensor triggering isrequired, the crush zone, or elsewhere such as the passengercompartment, the non-rush zone. Regardless of where sensors are mountedthere will always be crashes where the sensor triggers late and theoccupant has moved to a position near to the airbag deployment cover. Insuch cases, the occupant may be seriously injured or even killed by thedeployment of the airbag. This invention is largely concerned withpreventing such injuries and deaths by preventing late airbagdeployments.

In a Society of Automotive Engineers (SAE) paper by Mertz, Driscoll,Lenox, Nyquist and Weber titled “Response of Animals Exposed toDeployment of Various Passenger Inflatable Restraint System Concepts fora Variety of Collision Severities and Animal Positions” SAE 826074,1982, the authors show that an occupant can be killed or seriouslyinjured by the airbag deployment if he or she is located out of positionnear or against the airbag when deployment is initiated. Theseconclusions were again reached in a more recent paper by Lau, Horsch,Viano and Andrzejak titled “Mechanism of Injury From Air Bag DeploymentLoads”, published in Accident Analvsis & Prevention, Vol 25, No. 1,1993, Pergamnon Press, New York, where the authors conclude that “Evenan inflator with inadequate gas output to protect a properly seatedoccupant had sufficient energy to induce severe injuries in a surrogatein contact with the inflating module.” These papers highlight theimportance of preventing deployment of an airbag when an occupant is outof position and in close proximity to the airbag module.

The Ball-in-Tube crush zone sensor, such as disclosed in U.S. Pat. Nos.4,974,350; 4,198,864; 4,284,863; 4,329,549; 4,573,706 and 4,900,880 toD. S. Breed, has achieved the widest use while other technologies,including magnetically damped sensors as disclosed in U.S. Pat. No.4,933,515 to Behr et al and crush switch sensors such as disclosed inU.S. Pat. No. 4,995,639 to D. S. Breed, are now becoming available.Other sensors based on spring-mass technologies are also being used inthe crush zone. Crush zone mounted sensors, in order to functionproperly, must be located in the crush zone at the required trigger timeduring a crash or they can trigger late. One example of this wasdisclosed in a Society of Automotive Engineers (SAE) Paper by D.S. Breedand V. Castelli titled “Trends in Sensing Frontal Impacts”, SAE 890750,1989, and further in U.S. Pat. No. 4,900,880. In impacts with softobjects, the crush of a vehicle can be significantly less than forimpacts with barriers, for example. In such cases, even at moderatevelocity changes where an airbag might be of help in mitigatinginjuries, the crush zone mounted sensor might not actually be in thecrush zone at the time that sensor triggering is required for timelyairbag deployment, and as a result can trigger late when the occupant isalready resting against the airbag module.

There is a trend underway toward the implementation of Single PointSensors (SPS) which are typically located in the passenger compartment.In theory, these sensors use sophisticated computer algorithms todetermine that a particular crash is sufficiently severe as to requirethe deployment of an airbag. In another SAE paper by Breed, Sanders andCastelli titled “A Critique of Single Point Sensing”, SAE 920124, 1992,which is included herein by reference, the authors demonstrate thatthere is insufficient information in the non-crush zone of the vehicleto permit a decision to be made to deploy an airbag in time for manycrashes. Thus, sensors mounted in the passenger compartment or othernon-crush zone locations, will also trigger the deployment of the airbaglate on many crashes.

A crash sensor is necessarily a predictive device. In order to inflatethe airbag in time, the inflation must be started before the fullseverity of the crash has developed. All predictive devices are subjectto error, so that sometimes the airbag will be inflated when it is notneeded and at other times it will not be inflated when it could haveprevented injury. The accuracy of any predictive device can improvesignificantly when a longer time is available to gather and process thedata. One purpose of the occupant position sensor is to make possiblethis additional time in those cases where the occupant is farther fromthe steering wheel when the crash begins and/or where, due to seat beltuse or otherwise, the occupant is moving toward the steering wheel moreslowly. In these cases the decision on whether to deploy the airbag canbe deferred and a more precise determination made of whether the airbagis needed.

The discussions of timely airbag deployment above are all based on theseating position of the average male (the so called 50% male) relativeto the airbag or steering wheel. For the 50% male, the sensor triggeringrequirement is typically calculated based on an allowable motion of theoccupant of 5 inches before the airbag is fully inflated. Airbagstypically require about 30 milliseconds of time to achieve fullinflation and, therefore, the sensor must trigger inflation of theairbag 30 milliseconds before the occupant has moved forward 5 inches.The 50% male, however, is actually the 70% person and therefore about70% of the population sit on average closer to the airbag than the 50%male and thus are exposed to a greater risk of interacting with thedeploying airbag. A recent informal survey, for example, found thatalthough the average male driver sits about 12 inches from the steeringwheel, about 2% of the population of drivers sit closer tan 6 inchesfrom the steering wheel and 10% sit closer than 9 inches. Also, about 1%of drivers sit at about 24 inches and about 16% at least 18 inches fromthe steering wheel. None of the sensor or airbag systems now on themarket take account of this variation in occupant seating position andyet this can have a critical effect on the sensor required maximumtriggering time.

For example, if a fully inflated airbag is about 7 inches thick,measured from front to back, then any driver who is seated closer than 7inches will necessarily interact with the deploying airbag and theairbag probably should not be deployed at all. For a recently analyzed30 mph barrier crash of a midsized car, the sensor required triggeringtime, in order to allow the airbag to inflate fully before the driverbecomes closer than 7 inches from the steering wheel, results in amaximum sensing time of 8 milliseconds for an occupant initiallypositioned 9 inches from the airbag, 25 milliseconds at 12 inches, 45milliseconds at 18 inches and 57 milliseconds for the occupant who isinitially positioned at 24 inches from the airbag. Thus for the samecrash, the sensor required triggering time varies from a no trigger to57 milliseconds, depending on the initial position of the occupant. Asingle sensor triggering time criterion that fails to take this intoaccount, therefore, will cause injuries to small people or deny theprotection of the airbag to larger people. A very significantimprovement to the performance of an airbag system will necessarilyresult from taking the occupant position into account as describedherein.

A further complication results from the fact that a greater number ofoccupants are now wearing seatbelts which tends to prevent many of theseoccupants from getting too close to the airbag. Thus, just knowing theinitial position of the occupant is insufficient and either the positionmust be continuously monitored or the seatbelt use must be known. Also,the occupant may have fallen asleep or be unconscious prior to the crashand be resting against the steering wheel. Some sensor systems have beenproposed that double integrate the acceleration pulse in the passengercompartment and determine the displacement of the occupant based on thecalculated displacement of an unrestrained occupant seated at the midseating position. This sensor system then prevents the deployment of theairbag if, by this calculation, the occupant is too close to the airbag.This calculation can be greatly in error for the different seatingpositions discussed above and also for the seatbelted occupant, and thusan occupant who wears a seatbelt could be denied the added protection ofthe airbag in a severe crash.

As the number of vehicles which are equipped with airbags is now rapidlyincreasing, the incidence of late deployments is also increasing. It hasbeen estimated that out of approximately 400 airbag related complaintsto the National Highway Traffic Safety Administration (NHTSA) through1991, for example, about 5% to 10% involved burns and injuries whichwere due to late airbag deployments. There is also at least three knownfatalities where a late airbag deployment is suspected as the cause.

The need for an occupant position sensor has been observed by others andseveral methods have been disclosed in U.S. patents for determining theposition and velocity of an occupant of a motor vehicle. Each of thesesystems, however, have significant limitations. In White et al., U.S.Pat. No. 5,071,160, for example, a single acoustic sensor and detectoris disclosed and illustrated mounted lower than the steering wheel.White et al. correctly perceive that such a sensor could be defeated,and the airbag falsely deployed, by an occupant adjusting the controlknobs on the radio and thus they suggest the use of a plurality of suchtransmitter/receivers. If a driver of a vehicle is seated one foot fromthe transmitter/receiver, and using 1128 feet per second as the velocityof sound, it would require approximately 2 milliseconds for the sound totravel to the occupant and return. The use of the same device to bothtransmit and detect the sound waves requires that the device cannot sendand receive simultaneously and therefore it requires at least 2milliseconds to obtain a single observation of the occupant's position.Naturally, as the distance from the occupant to the sensor increases,the observation rate further decreases. For a passenger sitting two feetfrom the sensor, the delay is approximately 4 milliseconds. Sensors ofthis type can be used to accurately obtain the initial position of theoccupant but the determination of the occupant's velocity, and thus theprediction of when he/she is likely to be too close to the deployingairbag, will necessarily be inaccurate due to the long delay betweenposition points and thus the small number of such points available forthe prediction and the inherent noise in the reflected signal. Also,ultrasonic transducers send out a pulse that typically is about 0.2milliseconds long but, due to transducer ringing, this pulse can end toone millisecond. Furthermore, reflections continue to return to thetransducer for up to 6 to 10 milliseconds. Thus, updates from a singleranging transducer can only take place every 6 to 10 milliseconds.

Mattes et al. in U.S. Pat. No. 5,118,134 disclose a single ultrasonictransmitter and a separate receiver, but, no description is provided asto the manner in which this combination is used. In conventionalultrasonic distance measuring systems, the transmitter emits a burst ofultrasonic waves and then measures the time required for the waves tobounce off the object and reach the receptor. The transmitter does nottransmit again until the waves have been received by the receiver. Thissystem again suffers from the time delay of at least 6 to 10milliseconds described above.

Doppler techniques can be used to determine the velocity of the occupantas disclosed below. Both White et al. and Mattes et al., however,specifically state that the occupant's velocity is determined from asuccession of position measurements. The use of the Doppler effect isdisclosed in U.S. Pat. No. 3,275,975 to King, but only to determine thatthe occupant is not moving. No attempt is made by King to measure thevelocity of the occupant toward an airbag using this effect. Also noneof the references above disclose the use of an ultrasonic transmitterand receiver to simultaneously determine the position and velocity ofthe occupant using a combination of the transmission time and theDoppler effect as disclosed below.

The object of an occupant position sensor is to determine the locationof the head and/or chest of the vehicle occupant relative to the airbagsince it is the impact of either the head or chest with the deployingairbag which can result in serious injuries. For the purposes herein,therefore, whenever the position of the occupant is referenced it willmean the position of the head or chest of the occupant and not that ofhis/her arms, hands or legs. The preferred mounting of the ultrasonictransmitters, therefore, are those locations that have the clearestunimpeded view of the occupant's head and chest. These locations aregenerally at the top of the dashboard, the windshield, the headliner andthe rear view mirror. Both White et al. and Mattes et al. describe onlylower mounting locations of the ultrasonic transmitters such as on thedashboard or below the steeling wheel. Both such mounting locations areparticularly prone to detection errors due to positioning of theoccupant's hands, arms and legs. This would require at least three, andpreferably more, such sensors and detectors and an appropriate logiccircuitry for the case where the driver's arms are the closest objectsto two of the sensors. When an unimpeded view is not possible, somemeans of pattern recognition, which is not disclosed in the abovereferences, is required to differentiate between the occupant andhis/her extremities such as his/her hands, arms or legs.

Mattes et al. further describe the placement of the sensor in theheadrest but such an arrangement is insufficient since it measures thedistance from the headrest to the occupant and not from the airbag.

White et al. describes the use of error correction circuitry todifferentiate between the velocity of one of the occupant's hands as inthe case where he/she is adjusting the knob on the radio and theremainder of the occupant. Three ultrasonic sensors of the typedisclosed by White et al would accomplish this differentiation if two ofthem indicated that the occupant was not moving while the third wasindicating that he or she was. Such a combination, however, would notdifferentiate between an occupant with both hands and arms in the pathof the ultrasonic transmitter at such a location that it was blocking asubstantial view of the occupant's head or chest. Since the sizes anddriving positions of occupants are extremely varied, pattern recognitionsystems are required when a clear view of the occupant, unimpeded byhis/her extremities, newspapers, etc. cannot be guaranteed. Patternrecognition systems for the occupant as used here means any system whichwill differentiate between the occupant and his extremities based onrelative size, position or shape. Pattern recognition systems can alsobe used to differentiate an occupant from a seat or a bag of groceriesalso based on relative size, position or shape or even on passiveinfrared radiation, as described below.

OBJECTS AND SUMMARY OF THE INVENTION

The occupant position sensor of this invention is adapted forinstallation in the passenger compartment of an automotive vehicleequipped with a passenger protective device such as an inflatableairbag. When the vehicle is subjected to a crash of sufficient magnitudeas to require deployment of the passive protective device, and thesensor system has determined that the device is to be deployed, theoccupant position sensor and associated electronic circuitry determinesthe position of the vehicle occupant relative to the airbag and disablesdeployment of the airbag if the occupant is positioned so that he/she islikely to be injured by the deploying airbag. Naturally, as discussedbelow, the addition of an occupant position sensor onto a vehicle leadsto other possibilities such as the monitoring of the driver's behaviorwhich can be used to warn a driver if he or she is failing asleep, or tostop the vehicle if the driver loses the capacity to control thevehicle. According to a preferred implementation, an ultrasonicgenerator transmits a burst of ultrasonic waves which travel to theoccupant and are reflected back to a receptor, which may be the samedevice as the generator. The time period required for the waves totravel from the generator and return is used to determine the positionof the occupant and the frequency shift of the waves is used todetermine the velocity of the occupant relative to the airbag.

In another preferred implementation, infrared light is used toilluminate the occupant and lenses are used to focus images of theoccupant onto arrays of charge coupled devices (CCD). Outputs from theCCD arrays, are analyzed by appropriate logic circuitry, to determinethe position and velocity of the occupant's head and chest.

In yet another preferred implementation, a beam of radiation is movedback and forth across the occupant illuminating various portions of theoccupant and with appropriate algorithms the position of the occupant inthe seat is accurately determined.

In a simple implementation, other information such as seat positionand/or seatback position can be used with a buckle switch and/orseatbelt payout sensor to estimate the position of the occupant.

It is a principal object of this invention to provide an occupantposition sensor which reliably permits, and in a timely manner, adetermination to be made that he/she is out of position, or will becomeout of position, and likely to be-injured by a deploying airbag.

It is also a principal object of this invention to provide a systemwhich will accurately discriminate between the occupant's head or chestand other parts of the body in determining the occupant's position andvelocity.

It is another object of this invention to independently prevent thedeployment of the driver or passenger airbags if either occupant is outof position.

It is still another object of this invention to provide for a morecomplete analysis of an occupant through the use of CCD's, or CMOSarrays, to capture more of the occupants image.

Another object of this invention is to provide a warning to a driver ifhe/she is falling asleep.

Still another object of this invention is to sense that a driver isinebriated or otherwise suffering from a reduced capacity to operate amotor vehicle and to take appropriate action.

Yet another object of this invention is to provide a simplified systemfor determining the approximate location of a vehicle occupant and touse this system to control the deployment of the passive restraint. Thisoccupant position determining system can be based on the position of thevehicle seat, the position of the seat back, the state of the seatbeltbuckle switch, a seatbelt payout sensor or a combination of these.

In order to achieve some of these objects, in arrangements and methodfor determining the position of an occupant of a vehicle situated on aseat in accordance with the invention, the position of the seat and/or apart thereof is/are determined relative to a fixed point of reference tothereby enable a first approximation of the position of the occupant tobe obtained, e.g., by a processor including a look-up table, algorithmor other means for correlating the position of the seat and/or partthereof to a likely position of the occupant. More particularly, theposition of the seat portion of the seat and/or the back portion of theseat can be measured.

If only the first approximation of the position of the occupant isobtained then this is considered the likely actual position of theoccupant. However, to enhance the determination of the likely, actualposition of the occupant, the length of the seatbelt pulled out of theseatbelt retractor can be measured by an appropriate sensor such thatthe position of the occupant is obtained in consideration of theposition of the seat and the measured length of seatbelt pulled out ofthe seatbelt retractor. Also, a second approximation of the position ofthe occupant can be obtained, e.g., either by indirectly sensing theposition of the occupant of the seat or by directly sensing the positionof the occupant of the seat, such that the likely, actual position ofthe occupant is obtained in consideration of both approximations of theposition of the occupant. By “directly” sensing the position of theoccupant of the seat, it is meant that the position of the occupantitself is obtained by a detection of a property of the occupant withoutan intermediate measurement, e.g., a measurement of the position of theseat or the payout of the seatbelt, which must be correlated to theposition of the occupant. Sensing the position of the occupant by takingan intermediate measurement would constitute an “indirect” sensing ofthe position of the occupant of the seat. The second approximation canbe obtained by receiving waves from a space above the seat which areindicative of some aspect of the position of the occupant, e.g., thedistance between the occupant and the receiver(s). If required, wavesare transmitted into the space above the seat to be received by thereceiver(s). Possible mounting locations for the transmitter andreceiver(s) include proximate or attached to a rear view mirror of thevehicle, attached to the roof or headliner of the vehicle, on a steeringwheel of the vehicle, on an instrument panel of the vehicle and on acover of an airbag module.

Arrangements for controlling a deployable occupant restraint device in avehicle to protect an occupant m a seat in the vehicle during a crashinclude crash sensor means for determining whether deployment of theoccupant restraint device is required as a result of the crash, anoccupant position sensor arrangement for determining the position of theoccupant, and processor means coupled to the crash sensor means and theoccupant position sensor arrangement for controlling deployment of theoccupant restraint device based on the determination by the crash sensormeans if deployment of the occupant restraint device is required and theposition of the occupant. The occupant position sensor arrangementincludes seat position determining means for determining the position ofthe seat and/or a part thereof relative to a fixed point of reference tothereby enable a first approximation of the position of the occupant tobe obtained. In the absence of additional approximations of the positionof the occupant, the first approximation can be considered as theposition of the occupant. The position of the seat and/or part thereofmay be determined in any of the ways discussed above. The occupantposition sensor arrangement may include measuring means coupled to theprocessor means for measuring the length of the seatbelt pulled out ofthe seatbelt retractor such that the processor means control deploymentof the occupant restraint device based on the determination by the crashsensor means if deployment of the occupant restraint device is required,the position of the occupant and the measured length of seatbelt pulledout of the seatbelt retractor.

The occupant position sensor arrangement can also include means forproviding an additional approximation of the position of the occupant,either a direct sensing of the position of the occupant (a measurementof a property of the occupant) or an indirect sensing (a measurement ofa property of a component in the vehicle which can be correlated to theposition of the occupant), such that this approximation will be used inconjunction with the first approximation to provide a better estimate ofthe likely, actual position of the occupant. Such means may includereceiver means for receiving waves from a space above the seat andoptional transmitter means for transmitting waves into the space abovethe seat to be received by the receiver means. Possible mountinglocations for the transmitter means and receiver means include proximateor attached to a rear view mirror of the vehicle, attached to the roofor headliner of the vehicle, on a steering wheel of the vehicle, on aninstrument panel of the vehicle and on or proximate an occupantrestraint device, e.g., on or proximate a cover of an airbag module.

An additional factor to consider in the deployment of the occupantrestraint device is whether the seatbelt is buckled and thus in oneembodiment, the occupant position sensor arrangement includes meanscoupled to the processor means for determining whether the seatbelt isbuckled such that the processor means control deployment of the occupantrestraint device based on the determination by the crash sensor means ifdeployment of the occupant restraint device is required, the position ofthe occupant and the determination of whether the seatbelt is buckled.

Another arrangement for determining the position of an occupant of avehicle situated on a seat in the vehicle comprises occupant positionsensing means for obtaining a first approximation of the position of theoccupant, and confirmatory position sensing means for obtaining a secondapproximation of the position of the occupant such that a likely actualposition of the occupant is reliably determinable from the first andsecond approximations. The confirmatory position sensing means arearranged to measure the position of the seat and/or a part thereofrelative to a fixed point of reference and the length of a seatbeltpulled out of a seatbelt retractor. For example, the confirmatoryposition sensing means can be one or more sensors arranged to measurethe position of a seat portion of the seat, the position of a backportion of the seat and the length of the seatbelt pulled out of theseatbelt retractor.

Another arrangement for controlling a deployable occupant restraintdevice in a vehicle to protect an occupant in a seat in the vehicleduring a crash comprises crash sensor means for determining whetherdeployment of the occupant restraint device is required as a result ofthe crash, an occupant position sensor arrangement for determining theposition of the occupant and processor means coupled to the crash sensormeans and the occupant position sensor arrangement for controllingdeployment of the occupant restraint device based on the determinationby the crash sensor means if deployment of the occupant restraint deviceis required and the position of the occupant. The occupant positionsensor arrangement includes occupant position sensing means forobtaining a first approximation of the position of the occupant, andconfirmatory position sensing means for obtaining a second approximationof the position of the occupant such that the position of the occupantis reliably determinable from the first and second approximations. Theconfirmatory position sensing means are arranged to measure the positionof the seat and/or a part thereof relative to a fixed point of referenceand/or the length of a seatbelt pulled out of a seatbelt retractor. Theoccupant position sensor arrangement can also include means fordetermining whether the seatbelt is buckled in which case, the processormeans control deployment of the occupant restraint device based on basedon the determination by the crash sensor means if deployment of theoccupant restraint device is required, the position of the occupant andthe determination of whether the seatbelt is buckled.

Other objects and advantages of the present invention will becomeapparent from the following description of the preferred embodimentstaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the present inventionwill become apparent to one skilled in the art to which the inventionrelates upon consideration of the following detailed description of theinvention with reference to the accompanying drawings wherein

FIG. 1 is a side view, with certain portions removed or cut away, of aportion of the passenger compartment of a vehicle showing severalpreferred mounting locations of occupant position sensors for sensingthe position of the vehicle driver;

FIG. 2 is a cross section view of a steering wheel and airbag moduleassembly showing a preferred mounting location of an ultrasonic wavegenerator and receiver;

FIG. 3 is a side view, with certain portions removed or cut away, of aportion of the passenger compartment of a vehicle showing preferredmounting locations of the occupant position sensor employing multipletransmitters and receivers;

FIG. 4 is a side view, with certain portions removed or cut away, of aportion of the passenger compartment of a vehicle showing an occupantposition sensor used in combination with a reflective windshield forsensing the position of the vehicle passenger;

FIG. 5 is a partial cutaway view of a seatbelt retractor with a spoolout sensor utilizing a shaft encoder;

FIG. 6 is a side view of a portion of a seat and seat rail showing aseat position sensor utilizing a potentiometer;

FIG. 7 is a circuit schematic illustrating the use of the occupantposition sensor in conjunction with the remainder of the inflatablerestraint system; and

FIG. 8 is a schematic illustrating the circuit of an occupant positionsensing device using a modulated infrared signal, beat frequency andphase detector system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings wherein like reference numerals refer tothe same or similar elements, a section of the passenger compartment ofan automobile is shown generally as 100 in FIG. 1. A driver of a vehicle101 sits on a seat 102 behind a steering wheel 103 which contains anairbag assembly 104. Five transmitter and/or receiver assemblies 110,111, 112, 113 and 114 are positioned at various places in the passengercompartment to determine the location of the head, chest and torso ofthe driver relative to the airbag. Usually, in any given implementation,only three or four of the transmitters and receivers would be useddepending on their mounting locations as described below.

FIG. 1 illustrates several of the possible locations of such devices.For example, transmitter and receiver 110 emits ultrasonic acousticalwaves which bounce off the chest of the driver and return. Periodicallya burst of ultrasonic waves at about 50 kilohertz is emitted by thetransmitter/receiver and then the echo, or reflected signal, is detectedby the same or different device. An associated electronic circuitmeasures the time between the transmission and the reception of theultrasonic waves and thereby determines the distance from thetransmitter/receiver to the driver based on the velocity of sound. Thisinformation is then sent to the crash sensor and diagnostic circuitrywhich determines if the driver is close enough to the airbag that adeployment might, by itself, cause injury to the driver. In such a case,the circuit disables the airbag system and thereby prevents itsdeployment. In an alternate case, the sensor algorithm assesses theprobability that a crash requiring an airbag is in process and waitsuntil that probability exceeds an amount that is dependent on theposition of the occupant. Thus, for example, the sensor might decide todeploy the airbag based on a need probability assessment of 50%, if thedecision must be made immediately for an occupant approaching theairbag, but might wait until the probability rises to 95% for a moredistant occupant. Although a driver system has been illustrated, thepassenger system would be identical.

In another implementation, the sensor algorithm may determine the ratethat gas is generated to affect the rate that the airbag is inflated. Inall of these cases, the position of the occupant is used to affect thedeployment of the airbag either as to whether or not it should bedeployed at all, the time of deployment or as to the rate of inflation.

The ultrasonic transmitter/receiver 110 is similar to that used onmodern auto-focus cameras such as manufactured by the PolaroidCorporation. Other camera auto-focusing systems use differenttechnologies, which are also applicable here, to achieve the samedistance to object determination. One camera system manufactured by Fujiof Japan, for example, uses a stereoscopic system which could also beused to determine the position of a vehicle occupant providing there issufficient light available. In the case of insufficient light, a sourceof infrared light can be added to illuminate the driver. In a relatedimplementation, a source of infrared light is reflected off of thewindshield and illuminates the vehicle occupant. An infrared receiver114 is located attached to the rear view mirror 105, as shown in FIG. 1.Alternately, the infrared could be sent by the device 114 and receivedby a receiver elsewhere. Since any of the devices shown in FIGS. 1 and 3could be either transmitters, receivers or both, for simplicity, onlythe transmitted and not the reflected wave fronts are illustrated.

In the above described system, a lens within receptor 114 captures thereflected infrared light from the head or chest of the driver anddisplays it onto a charge coupled device (CCD) or CMOS array. One typeof CCD is that used in television cameras to convert an image into anelectrical signal. For the purposes herein, a CCD will be considered toinclude all devices which are capable of converting light frequencies,including infrared, into electrical signals including CMOS arrays. TheCCD is scanned and the focal point of the lens is altered, under controlof an appropriate circuit, until the sharpest image of the driver's heador chest results and the distance is then known from the focusingcircuitry. The precision of this measurement is enhanced if tworeceptors are used which can either project images onto a single CCD oronto separate CCDs. In the first case, one of the lenses could be movedto bring the two images into coincidence while in the other case thedisplacement of the images needed for coincidence would be determinedmathematically. Naturally, other systems could be used to keep track ofthe different images such as the use of filters creating differentinfrared frequencies for the different receptors and again using thesame CCD array. In addition to greater precision in determining thelocation of the occupant, the separation of the two receptors can alsobe used to minimize the effects of hands, arms or other extremitieswhich might be very close to the airbag. In this case, where thereceptors are mounted high on the dashboard on either side of thesteering wheel, an arm, for example, would show up as a thin object butmuch closer to the airbag than the larger body parts and, therefore,easily distinguished and eliminated, permitting the sensors to determinethe distance to the occupant's chest. This is one example of the use ofpattern recognition.

An optical infrared transmitter and receiver assembly is shown generallyat 112 in FIG. 1 and is mounted onto the instrument panel facing thewindshield. Although not shown in this view, reference 112 consists ofthree devices, one transmitter and two receivers, one on each side ofthe transmitter. In this case, the windshield is used to reflect theinfrared radiation, and also the radiation reflected back by the driver,in a manner similar to the “heads-up” display which is now being offeredon several automobile models. The “heads-up” display, of course, iscurrently used only to display information to the driver and is not usedto reflect light from the driver to a receiver. In this case, thedistance to the driver may be determined stereoscopically through theuse of the two receivers. In its most elementary sense, this system canbe used to measure the distance of the driver to the airbag module. Inmore sophisticated applications, the position of the driver, andparticularly of the driver's head, can be monitored over time and anybehavior, such as a drooping head, indicative of the driver fallingasleep or of being incapacitated by drugs, alcohol or illness can bedetected and appropriate action taken. Other forms of radiationincluding visual light, radar and microwaves as well as high frequencyultra sound could also be used by those skilled in the art.

Particular mention should be made of the use of radar since inexpensivesingle axis antennas are now readily available. A scanning radar beam isused in this implementation and the reflected signal is received by asingle axis phase array antenna to generate an image of the occupant forinput into the appropriate pattern detection circuitry, which should beconsidered to include, inter alia, different forms of sensor fusion. Theword circuitry as used herein includes, in addition to normal electroniccircuits, a microprocessor and appropriate software.

Electromagnetic or ultrasonic energy can be transmitted in three modesin determining the position of an occupant. In most of the casesdisclosed above, it is assumed that the energy will be transmitted in abroad diverging beam which interacts with a substantial portion of theoccupant. This method has the disadvantage that it will reflect firstoff the nearest object and, especially if that object is close to thetransmitter, it may mask the true position of the occupant. This can bepartially overcome through the use of the second mode which uses anarrow beam. In this case, several narrow beams are used. These beamsare aimed in different directions toward the occupant from a positionsufficiently away from the occupant that interference is unlikely. Asingle receptor could be used providing the beams are either cycled onat different times or are of different frequencies. Another approach isto use a single beam emanating from a location which has an unimpededview of the occupant such as the windshield header or headliner. If twospaced apart CCD array receivers are used, the angle of the reflectedbeam can be determined and the location of the occupant can becalculated. The third mode is to use a single beam in a manner so thatit scans back and forth or up and down, or in some other pattern, acrossthe occupant. In this manner, an image of the occupant can be obtainedusing a single receptor and pattern recognition software can be used tolocate the head or chest of the occupant. The beam approach is mostapplicable to electromagnetic energy but high frequency ultra sound canalso be formed into a narrow beam.

The windshield header as used herein includes the space above the frontwindshield including the first few inches of the roof. The headliner isthe roof interior cover that extends back from the header.

A similar effect to modifying g the wave transmission mode can also beobtained by varying the characteristics of the receptors. Throughappropriate lenses or reflectors, receptors can be made to be mostsensitive to radiation emitted from a particular direction. In thismanner, a single broad beam transmitter can be used coupled with anarray of focused receivers to obtain a rough image of the occupant.

Each of these methods of transmission or reception could be used, forexample, at any of the preferred mounting locations shown in FIG. 1.

Another preferred location of a transmitter/receiver for use withairbags is shown at 111 in FIG. 1. In this case, the device is attachedto the steering wheel and gives an accurate determination of thedistance of the driver's chest from the airbag module. Thisimplementation could be used with another device such as 110 at anotherlocation.

Alternate mountings for the transmitter/receiver include variouslocations on the instrument panel on either side of the steering columnsuch as 113 in FIG. 1. Also, although some of the devices hereinillustrated assume that for the ultrasonic system the same device wouldbe used for both transmitting and receiving waves, there are advantagesin separating these functions. Since there is a time lag required forthe system to stabilize after transmitting a pulse before it can receivea pulse, close measurements are enhanced, for example, by using separatetransmitters and receivers. In addition, if the ultrasonic transmitterand receiver are separated, the transmitter can transmit continuouslyproviding the transmitted signal is modulated in such a manner that thereceived signal can be compared with the transmitted signal to determinethe time it took for the waves to reach and reflect off of the occupant.Many methods exist for this modulation including varying the frequencyor amplitude of the waves or by pulse modulation or coding. In allcases, the logic circuit which controls the sensor and receiver must beable to determine when the signal which was most recently received wastransmitted. In this manner, even though the time that it takes for thesignal to travel from the transmitter to the receiver, via reflectionoff of the occupant, may be several milliseconds, information as to theposition of the occupant is received continuously which permits anaccurate, although delayed, determination of the occupant's velocityfrom successive position measurements. Conventional ultrasonic distancemeasuring devices must wait for the signal to travel to the occupant andreturn before a new signal is sent. This greatly limits the frequency atwhich position data can be obtained to the formula where the frequencyis equal to the velocity of sound divided by two times the distance tothe occupant. For example, if the velocity of sound is taken at about1000 feet per second, occupant position data for an occupant located onefoot from the transmitter can only be obtained every 2 millisecondswhich corresponds to a frequency of 500 cycles per second.

This slow frequency that data can be collected seriously degrades theaccuracy of the velocity calculation. The reflection of ultrasonic wavesfrom the clothes of an occupant, for example, can cause noise or scatterin the position measurement and lead to significant inaccuracies in agiven measurement. When many measurements are taken more rapidly, as inthe technique described here, these inaccuracies can be averaged and asignificant improvement in the accuracy of the velocity calculationresults.

The determination of the velocity of the occupant need not be derivedfrom successive distance measurements. A potentially more accuratemethod is to make use of the Doppler effect where the frequency of thereflected waves differs from the transmitted waves by an amount which isproportional to the occupant's velocity. In a preferred embodiment ofthe present invention, a single ultrasonic transmitter and a separatereceiver are used to measure the position of the occupant, by the traveltime of a known signal, and the velocity, by the frequency shift of thatsignal. Although the Doppler effect has been used to determine whetheran occupant has fallen asleep as disclosed in the U.S. patent to Kingreferenced above, it has not heretofore been used in conjunction with aposition measuring device to determine whether an occupant is likely tobecome out of position and thus in danger of being injured by adeploying airbag. This combination is particularly advantageous sinceboth measurements can be accurately and efficiently determined using asingle transmitter and receiver pair resulting in a low cost system.

One problem with Doppler measurements is the slight change in frequencythat occurs during normal occupant velocities. This requires thatsophisticated electronic techniques be utilized to increase thefrequency and thereby render it easier to measure the velocity using thephase shift. For many implementations, therefore, the velocity of theoccupant is determined by calculating the difference between successiveposition measurements.

Another preferred embodiment of this invention makes use of radio wavesand a voltage controlled oscillator (VCO). In this implementation, thefrequency of the oscillator is controlled through the use of a phasedetector which adjusts the oscillator frequency so that exactly one halfwave occupies the distance from the transmitter to the receiver viareflection off of the occupant. The adjusted frequency is thus inverselyproportional to the distance from the transmitter to the occupant.Alternately, an FM phase discriminator can be used as known to thoseskilled in the art. These systems could be used in any of the locationsillustrated in FIG. 1.

It was suggested in the U.S. patent to Mattes et al. discussed above,that a passive infrared system could be used to determine the positionof an occupant relative to an airbag. Passive infrared measures theinfrared radiation emitted by the occupant and compares it to thebackground. As such, unless it is coupled with a pattern recognitionsystem, it can best be used to determine that an occupant is movingtoward the airbag since the amount of infrared radiation would then beincreasing. Therefore, it could be used to estimate the velocity of theoccupant but not his/her position relative to the airbag, since theabsolute amount of such radiation will depend on the occupant's size,temperature and clothes as well as on his position. When passiveinfrared is used in conjunction with another distance measuring system,such as the ultrasonic system described above, the combination would becapable of determining both the position and velocity of the occupantrelative to the airbag. Such a combination would be economical sinceonly the simplest circuits would be required. In one implementation, forexample, a group of waves from an ultrasonic transmitter could be sentto an occupant and the reflected group received by a receiver. Thedistance to the occupant would be proportional to the time between thetransmitted and received groups of waves and the velocity determinedfrom the passive infrared system. This system could be used in any ofthe locations illustrated in FIG. 1 as well as others not illustrated.

Passive infrared could also be used effectively in conjunction with apattern recognition system. In this case, the passive infrared radiationemitted from an occupant can be focused onto a CCD array and analyzedwith appropriate pattern recognition circuitry, or software, todetermine the position of the occupant. Such a system could be mountedat any of the preferred mounting locations shown in FIG. 1 as well asothers not illustrated.

A transmitter/receiver 215 shown mounted on the cover of the airbagmodule is shown in FIG. 2. The transmitter/receiver 215 is attached tovarious electronic circuitry, not shown, by means of wire cable 212.When an airbag deploys, the cover 220 begins moving toward the driver.If the driver is in close proximity to this cover during the earlystages of deployment, the driver can be seriously injured or evenkilled. It is important, therefore, to sense the proximity of the driverto the cover and if he or she gets too close, to disable deployment ofthe airbag. An accurate method of obtaining this information would be toplace the distance measuring device onto the airbag cover as is shown inFIG. 2. Appropriate electronic circuitry can be used to not onlydetermine the actual distance of the driver from the cover but also hisvelocity as discussed above. In this manner, a determination can be madeas to where the driver is likely to be at the time of deployment of theairbag. This information can be used most importantly to preventdeployment but can also be used to modify the rate of airbag deployment.In FIG. 2, for one implementation, ultrasonic waves are transmitted by atransmitter/receiver 215 toward the chest 222 of the driver. Thereflected waves are then received by the same transmitter/receiver 215.

One problem of the system using a sensor 111 in FIG. 1 or sensor 215 asshown in FIG. 2 is that a driver may have inadvertently placed his handover the transmitter/receiver 111 or 215, thus defeating the operationof the device. A second confirming transmitter/receiver 110 is thereforeplaced at some other convenient position such as on the roof orheadliner of the passenger compartment as shown in FIG. 3. Thistransmitter/receiver operates in a manner similar to 111 and 215.

A more complicated and sophisticated system is shown conceptually inFIG. 4 where transmitter/receiver assembly 112 is illustrated. In thiscase, as described briefly above, an infrared transmitter and a pair ofoptical receivers are used to capture the reflection of the passenger.When this system is used to monitor the driver as shown in FIG. 4, withappropriate circuitry and a microprocessor, the behavior of the drivercan be monitored. Using this system, not only can the position andvelocity of the driver be determined and used in conjunction with anairbag system, but it is also possible to determine whether the driveris falling asleep or exhibiting other potentially dangerous behavior bycomparing portions of his/her image over time. In this case, the speedof the vehicle can be reduced or the vehicle even stopped if this actionis considered appropriate. This implementation has the highestprobability of an unimpeded view of the driver since he/she must have aclear view through the windshield in order to operate the motor vehicle.

As discussed above, a primary object of this invention is to provideinformation as to the location of the driver, or other vehicle occupant,relative to the airbag, to appropriate circuitry which will process thisinformation and make a decision as to whether to prevent deployment ofthe airbag in a situation where it would otherwise be deployed, orotherwise affect the time of deployment. One method of determining theposition of the driver as discussed above is to actually measure his orher position either using microwaves, optics or acoustics. An alternateapproach, which is preferably used to confirm the measurements made bythe systems described above, is to use information about the position ofthe seat and the seatbelt spool out to determine the likely location ofthe driver relative to the airbag. To accomplish this, the length ofbelt material which has been pulled out of the seatbelt retractor can bemeasured using conventional shaft encoder technology using eithermagnetic or optical systems. An example of an optical encoder isillustrated generally as 501 in FIG. 5. It consists of an encoder disk502 and a receptor 503 which sends a signal to appropriate circuitryevery time a line on the encoder disk passes by the receptor.

In a similar manner, the position of the seat can be determined througheither a linear encoder or a potentiometer as illustrated in FIG. 6. Inthis case, a potentiometer 601 is positioned along the seat track 602and a sliding brush assembly 603 is used with appropriate circuitry todetermine the fore and aft location of the seat 610. Naturally, forthose seats which permit the seat back angle to be adjusted, a similarmeasuring system 604 would be used to determine the angle of the seatback. In this manner, the position of the seat relative to the airbagmodule can be determined. This information can be used in conjunctionwith the seatbelt spool out sensor to confirm the approximate positionof the chest of the driver relative to the airbag.

For a simplified occupant position measuring system, a combination ofseatbelt spool out sensor, seat belt buckle sensor, seat back positionsensor, and seat position sensor (the “seat” in this last case meaningthe seat portion) can be used either together or as a subset of suchsensors to make an approximation as to the location of the driver orpassenger in the vehicle. This information can be used to confirm themeasurements of the ultrasonic and infrared sensors or as a stand-alonesystem. Naturally, as a stand-alone system it will not be as an accurateas systems using ultrasonics or electromagnetics. Since a significantnumber of fatalities involve occupants who are not wearing seatbelts,and since accidents frequently involved significant pre-crash maneuversand breaking that can cause at least the vehicle passenger to be thrownout of position, this system has serious failure modes. Nevertheless,sensors that measure seat position, for example, are available now andthis system permits immediate introduction of a crude occupant positionsensing system immediately and therefore it has great value. One suchsimple system, employs a seat position sensor only. For the driver, forexample, if the seat is in the forwardmost position, then it makes nosense to deploy the driver airbag at full power. Instead, either adepowered deployment or no deployment would be called for in many crashsituations.

For most cases, the seatbelt spool out sensor would be sufficient togive a good confirming indication of the position of the occupant'schest regardless of the position of the seat and seat back. This isbecause the seatbelt is usually attached to the vehicle at least at oneend. In some cases, especially where the seat back angle can beadjusted, separate retractors would be used for the lap and shoulderportions of the seatbelt and the belt would not be permitted to slipthrough the “D-ring”. The length of belt spooled out from the shoulderbelt retractor then becomes a very good confirming measure of theposition of the occupant's chest.

The occupant position sensor in any of its various forms can beintegrated into the airbag system circuitry as shown schematically inFIG. 7. In this example, the occupant position sensors are used as aninput to a 'smart electronic sensor and diagnostic system. Theelectronic sensor determines whether the airbag should be deployed basedon the vehicle acceleration crash pulse, or crush zone mounted crashsensors, and the occupant position sensor determines whether theoccupant is too close to the airbag and therefore that the deploymentshould not take place.

A particular implementation of an occupant position sensor having arange of from 0 to 2 meters (corresponding to an occupant position offrom 0 to 1 meter since the signal must travel both to and from theoccupant) using infrared is illustrated in the block diagram schematicof FIG. 8. The operation is as follows. A 48 MHz signal, f1, isgenerated by a crystal oscillator 801 and fed into a frequency tripler802 which produces an output signal at 1.44 MHz. The 1.44 MHz signal isthen fed into an infrared diode driver 803 which drives the infrareddiode 804 causing it to emit infrared light modulated at 144 MHz and areference phase angle of zero degrees. The infrared diode 804 isdirected at the vehicle occupant. A second signal f2 having a frequencyof 48.05 MHz, which is slightly greater than f1, is also fed into afrequency tripler 806 to create a frequency of 144.15 MHz. This signalis then fed into a mixer 807 which combines it with the 144 MHz signalfrom frequency tripler 802. The combined signal from the mixer 807 isthen fed to filter 808 which removes all signals except for thedifference, or beat frequency, between 3 times f1 and 3 times f2, of 150kHz. The infrared signal which is reflected from the occupant isreceived by receiver 809 and fed into pre-amplifier 811. This signal hasthe same modulation frequency, 144 MHz, as the transmitted signal butnow is out of phase with the transmitted signal by an angle x due to thepath that the signal took from the transmitter to the occupant and backto the receiver. The output from pre-amplifier 811 is fed to a secondmixer 812 along with the 144.15 MHz signal from the frequency tripler806. The output from mixer 812 is then amplified by the automatic gainamplifier 813 and fed into filter 814. The filter 814 eliminates allfrequencies except for the 150 kHz difference, or beat, frequency in asimilar manner as was done by filter 808. The resulting 150 kHzfrequency, however, now has a phase angle x relative to the signal fromfilter 808. Both 150 kHz signals are now fed into a phase detector 815which determines the magnitude of the phase angle x. It can be shownmathematically that, with the above values, the distance from thetransmitting diode to the occupant is x/345.6 where x is measured indegrees and the distance in meters.

The applications described herein have been illustrated using the driverof the vehicle. Naturally the same systems of determining the positionof the occupant relative to the airbag apply to the passenger, sometimesrequiring minor modifications. It is likely that the sensor requiredtriggering time based on the position of the occupant will be differentfor the driver than for the passenger. Current systems are basedprimarily on the driver with the result that the probability of injuryto the passenger is necessarily increased either by deploying the airbagtoo late or by failing to deploy the airbag when the position of thedriver would not warrant it but the passenger's position would. With theuse of occupant position sensors for both the passenger and driver, theairbag system can be individually optimized for each occupant and resultin further significant injury reduction. In particular, either thedriver or passenger system can be disabled if either the driver orpassenger is out of position.

There is almost always a driver present in vehicles that are involved inaccidents where an airbag is needed. Only about 30% of these vehicles,however, have a passenger. If the passenger is not present, there isusually no need to deploy the passenger side airbag. The occupantposition sensor, when used for the passenger side with proper patternrecognition circuitry, can also ascertain whether or not the seat isoccupied, and if not, can disable the deployment of the passenger sideairbag and thereby save the cost of its replacement. A sophisticatedpattern recognition system could even distinguish between an occupantand a bag of groceries, for example. Finally, there has been muchwritten about the out of position child who is standing or otherwisepositioned adjacent to the airbag, perhaps due to pre-crash braking.Naturally, the occupant position sensor described herein can prevent thedeployment of the airbag in this situation.

There has thus been shown and described an occupant position sensorwhich fulfills all the objects and advantages sought after. Manychanges, modifications, variations and other uses and applications ofthe subject invention will, however, become apparent to those skilled inthe art after considering this specification and the accompanyingdrawings which disclose the preferred embodiments thereof. All suchchanges, modifications, variations and other uses and applications whichdo not depart from the spirit and scope of the invention are deemed tobe covered by the invention which is limited only by the followingclaims.

What is claimed is:
 1. In combination, a vehicle and an arrangement fordetermining the position of an occupant situated on a seat in thevehicle, the arrangement comprising: seat position determining means fordetermining the position of the seat or a part thereof relative to afixed point of reference, occupant position sensing means arranged apartfrom the seat for sensing the position of the occupant of the seat andproviding a first approximation of the position of the occupant, and aprocessor coupled to said seat position determining means and saidoccupant position sensing means for determining the position of theoccupant in consideration of the position of the seat or part thereof asdetermined by said seat position determining means and the firstapproximation of the position of the occupant from said occupantposition sensing means.
 2. The arrangement of claim 1, wherein saidprocessor determines a second approximation of the position of theoccupant based on the position of the seat or part thereof as determinedby said seat position determining means.
 3. The arrangement of claim 1,wherein the seat includes a seat portion and a back portion, said seatposition determining means comprising at least one of a sensor formeasuring the position of the seat portion of the seat and a sensor formeasuring the position of the back portion of the seat.
 4. Thearrangement of claim 1, wherein the seat includes a seat track mountedto the vehicle, said seat position determining means comprising apotentiometer positioned along the seat track and a sliding brushassembly coupling the seat to the seat track and engaging with saidpotentiometer.
 5. The arrangement of claim 1, wherein the seat includesa seatbelt and a seatbelt retractor, further comprising measuring meansfor measuring the length of the seatbelt pulled out of the seatbeltretractor, said processor being structured and arranged to determine theposition of the occupant in consideration of the position of the seat orpart thereof as determined by said seat position determining means, thefirst approximation of the position of the occupant from said occupantposition sensing means and the measured length of seatbelt pulled out ofthe seatbelt retractor when the seatbelt is pulled out of the seatbeltretractor.
 6. The arrangement of claim 5, wherein said measuring meanscomprise an encoder and circuitry for processing information from saidencoder.
 7. The arrangement of claim 1, wherein said occupant positionsensing means are arranged in a windshield header of the vehicle.
 8. Thearrangement of claim 1, wherein said occupant position sensing meanscomprise receiver means for receiving waves from a space above the seat.9. The arrangement of claim 8, wherein said receiver means arestructured and arranged to convert waves into electrical signals, saidoccupant position sensing means further comprising processor means forreceiving the electrical signals from said receiver means and derivingthe first approximation of the position of the occupant from theelectrical signals.
 10. The arrangement of claim 8, wherein saidreceiver means are structured and arranged to receive infraredradiation.
 11. The arrangement of claim 8, wherein said receiver meansare arranged such that the waves received by said receiver means travelin a first direction from the space above the seat toward a windshieldof a vehicle in which the seat is situated, reflect off of thewindshield and then travel in a second direction toward said receivermeans.
 12. The arrangement of claim 8, wherein said receiver means areattached to a rear view mirror of the vehicle.
 13. The arrangement ofclaim 8, wherein said receiver means are attached to the roof orheadliner of the vehicle.
 14. The arrangement of claim 8, wherein saidreceiver means are arranged on a steering wheel of the vehicle.
 15. Thearrangement of claim 8, wherein said receiver means are arranged on aninstrument panel of the vehicle.
 16. The arrangement of claim 8, whereinsaid receiver means are arranged on a cover of an airbag module or on oradjacent to the airbag module.
 17. The arrangement of claim 8, whereinsaid receiver means comprise a plurality of receivers, the firstapproximation of the position of occupant being determined bytriangulation.
 18. The arrangement of claim 8, wherein said occupantposition sensing means further comprise transmitter means fortransmitting waves into the space above the seat, said receiver meansbeing arranged to receive the waves transmitted by said transmittermeans and modified by passing through the space above the seat.
 19. Thearrangement of claim 18, wherein said transmitter means are structuredand arranged to transmit electromagnetic waves and said receiver meansare structured and arranged to convert electromagnetic waves intoelectrical signals, said occupant position sensing means furthercomprising means for receiving the electrical signals from said receivermeans and deriving the first approximation of the position of theoccupant from the electrical signals.
 20. The arrangement of claim 18,wherein said transmitter means are structured and arranged to transmitinfrared radiation and said receiver means are structured and arrangedto receive infrared radiation.
 21. The arrangement of claim 18, whereinsaid transmitter means are arranged such that the waves transmitted bysaid transmitter means travel in a first direction toward a windshieldof a vehicle in which the seat is situated, reflect off of thewindshield and then travel in a second direction toward the space abovethe seat.
 22. The arrangement of claim 18, wherein at least one of saidtransmitter means and said receiver means is attached to a rear viewmirror of the vehicle.
 23. The arrangement of claim 18, wherein at leastone of said transmitter means and said receiver means is attached to theroof or headliner of the vehicle.
 24. The arrangement of claim 18,wherein at least one of said transmitter means and said receiver meansis arranged on a steering wheel of the vehicle.
 25. The arrangement ofclaim 18, wherein at least one of said transmitter means and saidreceiver means is arranged on an instrument panel of the vehicle. 26.The arrangement of claim 18, wherein at least one of said transmittermeans and said receiver means is arranged on a cover of an airbag moduleor on or adjacent to the airbag module.
 27. The arrangement of claim 8,wherein said receiver means are positioned to be operative rearward inorder to receive waves from a rear of the vehicle.
 28. The arrangementof claim 8, wherein said occupant position sensing means are arranged onthe roof of the vehicle adjacent the front windshield.
 29. Thearrangement of claim 8, wherein said occupant position sensing means arearranged at a front of the passenger compartment.
 30. In combination, avehicle and an arrangement for determining the position of an occupantof a vehicle situated on a seat in the vehicle, the seat having anassociated seatbelt and seatbelt retractor, the arrangement comprising:occupant position sensing means arranged apart from the seat forobtaining a first approximation of the position of the occupant, andconfirmatory position sensing means for obtaining a second approximationof the position of the occupant such that the position of the occupantis reliably determinable from the first and second approximations, saidconfirmatory position sensing means being arranged to measure at leastone of the position of the seat or a part thereof relative to a fixedpoint of reference and the length of the seatbelt pulled out of theseatbelt retractor.
 31. The arrangement of claim 30, wherein saidconfirmatory position sensing means measure the position of a seatportion of the seat.
 32. The arrangement of claim 30, wherein saidconfirmatory position sensing means measure the position of a backportion of the seat.
 33. The arrangement of claim 30, wherein saidconfirmatory position sensing means measure the length of the seatbeltpulled out of the seatbelt retractor.
 34. A method for determining theposition of an occupant of a vehicle situated on a seat in the vehicle,comprising the steps of: determining the position of the seat or a partthereof relative to a fixed point of reference, obtaining a firstapproximation of the position of the occupant from the determinedposition of the seat or part thereof, sensing the position of theoccupant of the seat by means situated apart from the seat to obtain asecond approximation of the position of the occupant, and utilizing thesecond approximation of the position of the occupant in combination withthe first approximation of the position of the occupant to determine theposition of the occupant in the vehicle.
 35. The method of claim 34,wherein the step of determining the position of the seat or part thereofcomprises the step of measuring the position of a seat portion of theseat.
 36. The method of claim 34, wherein the step of determining theposition of the seat or part thereof comprises the step of measuring theposition of a back portion of the seat.
 37. The method of claim 34,further comprising the steps of: measuring the length of a seatbeltpulled out of a seatbelt retractor associated with the seat, andutilizing the measured length of seatbelt pulled out of the seatbeltretractor in combination with the first and second approximations of theposition of the occupant to determine the position of the occupant inthe vehicle.
 38. The method of claim 34, wherein the step of sensing theposition of the occupant comprises the step of receiving waves from aspace above the seat.
 39. The method of claim 38, wherein the step ofsensing the position of the occupant further comprises the step oftransmitting waves into the space above the seat whereby the transmittedwaves are modified by passing through the space above the seat and thenreceived.
 40. A method for determining the position of an occupant of avehicle situated on a seat in the vehicle, comprising the steps of:obtaining a first approximation of the position of the occupant bymeasuring at least one of the position of the seat or a part thereofrelative to a fixed point of reference and the length of a seatbeltpulled out of a seatbelt retractor, obtaining a second approximation ofthe position of the occupant by means situated apart from the seat, andutilizing the first and second approximations to provide a likely,actual position of the occupant.
 41. In combination, a vehicle and anarrangement for determining the position of an occupant situated on aseat in the vehicle, the seat including a seatbelt and a seatbeltretractor, the arrangement comprising: seat position determining meansfor determining the position of the seat or a part thereof relative to afixed point of reference, and measuring means for measuring the lengthof the seatbelt pulled out of the seatbelt retractor, the position ofthe occupant being obtainable in consideration of the position of theseat or part thereof as determined by said seat position determiningmeans and the measured length of seatbelt pulled out of the seatbeltretractor when the seatbelt is pulled out of the seatbelt retractor. 42.The arrangement of claim 41, wherein said measuring means comprise anencoder and circuitry for processing information from said encoder. 43.In combination, a vehicle and an arrangement for determining theposition of an occupant situated on a seat in the vehicle, thearrangement comprising: seat position determining means for determiningthe position of the seat or a part thereof relative to a fixed point ofreference, and occupant position sensing means for sensing the positionof the occupant of the seat, the position of the occupant beingobtainable in consideration of the position of the seat or part thereofas determined by said seat position determining means and the positionof the occupant as sensed by said occupant position sensing means, saidoccupant position sensing means comprising receiver means for receivingwaves from a space above the seat, said receiver means being arrangedsuch that the waves received by said receiver means travel in a firstdirection from the space above the seat toward a windshield of a vehiclein which the seat is situated, reflect off of the windshield and thentravel in a second direction toward said receiver means.
 44. Incombination, a vehicle and an arrangement for determining the positionof an occupant situated on a seat in the vehicle, the arrangementcomprising: seat position determining means for determining the positionof the seat or a part thereof relative to a fixed point of reference,and occupant position sensing means for sensing the position of theoccupant of the seat, the position of the occupant being obtainable inconsideration of the position of the seat or part thereof as determinedby said seat position determining means and the position of the occupantas sensed by said occupant position sensing means, said occupantposition sensing means comprising receiver means for receiving wavesfrom a space above the seat, said receiver means being arranged on asteering wheel of the vehicle.
 45. In combination, a vehicle and anarrangement for determining the position of an occupant situated on aseat in the vehicle, the arrangement comprising: seat positiondetermining means for determining the position of the seat or a partthereof relative to a fixed point of reference, and occupant positionsensing means for sensing the position of the occupant of the seat, theposition of the occupant being obtainable in consideration of theposition of the seat or part thereof as determined by said seat positiondetermining means and the position of the occupant as sensed by saidoccupant position sensing means, said occupant position sensing meanscomprising receiver means for receiving waves from a space above theseat, said receiver means being arranged on or adjacent an airbagmodule.
 46. In combination, a vehicle and an arrangement for determiningthe position of an occupant situated on a seat in the vehicle, thearrangement comprising: seat position determining means for determiningthe position of the seat or a part thereof relative to a fixed point ofreference, and occupant position sensing means for sensing the positionof the occupant of the seat, the position of the occupant beingobtainable in consideration of the position of the seat or part thereofas determined by said seat position determining means and the positionof the occupant as sensed by said occupant position sensing means, saidoccupant position sensing means comprising receiver means for receivingwaves from a space above the seat, said receiver means comprising aplurality of receivers, the position of occupant being determined bytriangulation.
 47. In combination, a vehicle and an arrangement fordetermining the position of an occupant situated on a seat in thevehicle, the arrangement comprising: seat position determining means fordetermining the position of the seat or a part thereof relative to afixed point of reference, and occupant position sensing means forsensing the position of the occupant of the seat, the position of theoccupant being obtainable in consideration of the position of the seator part thereof as determined by said seat position determining meansand the position of the occupant as sensed by said occupant positionsensing means, said occupant position sensing means comprising receivermeans for receiving waves from a space above the seat and transmittermeans for transmitting waves into the space above the seat, saidreceiver means being arranged to receive the waves transmitted by saidtransmitter means and modified by passing through the space above theseat, said transmitter means being arranged such that the wavestransmitted by said transmitter means travel in a first direction towarda windshield of a vehicle in which the seat is situated, reflect off ofthe windshield and then travel in a second direction toward the spaceabove the seat.
 48. In combination, a vehicle and an arrangement fordetermining the position of an occupant situated on a seat in thevehicle, the arrangement comprising: seat position determining means fordetermining the position of the seat or a part thereof relative to afixed point of reference, and occupant position sensing means forsensing the position of the occupant of the seat, the position of theoccupant being obtainable in consideration of the position of the seator part thereof as determined by said seat position determining meansand the position of the occupant as sensed by said occupant positionsensing means, said occupant position sensing means comprising receivermeans for receiving waves from a space above the seat and transmittermeans for transmitting waves into the space above the seat, saidreceiver means being arranged to receive the waves transmitted by saidtransmitter means and modified by passing through the space above theseat said transmitter means being arranged on a steering wheel of thevehicle.
 49. In combination, a vehicle and an arrangement fordetermining the position of an occupant situated on a seat in thevehicle, the arrangement comprising: seat position determining means fordetermining the position of the seat or a part thereof relative to afixed point of reference, and occupant position sensing means forsensing the position of the occupant of the seat, the position of theoccupant being obtainable in consideration of the position of the seator part thereof as determined by said seat position determining meansand the position of the occupant as sensed by said occupant positionsensing means, said occupant position sensing means comprising receivermeans for receiving waves from a space above the seat and transmittermeans for transmitting waves into the space above the seat, saidreceiver means being arranged to receive the waves transmitted by saidtransmitter means and modified by passing through the space above theseat, said transmitter means being arranged on or adjacent an airbagmodule.
 50. In combination, a vehicle and an arrangement for determiningthe position of an occupant situated on a seat in the vehicle, thearrangement comprising: seat position determining means for determiningthe position of the seat or a part thereof relative to a fixed point ofreference; occupant position sensing means for sensing the position ofthe occupant of the seat and providing a first approximation of theposition of the occupant, said occupant position sensing meanscomprising receiver means for receiving waves from a space above theseat; and a processor coupled to said seat position determining meansand said occupant position sensing means for determining the position ofthe occupant in consideration of the position of the seat or partthereof as determined by said seat position determining means and thefirst approximation of the position of the occupant from said occupantposition sensing means.
 51. In combination, a vehicle and an arrangementfor determining the position of an occupant of a vehicle situated on aseat in the vehicle, the seat having an associated seatbelt and seatbeltretractor, the arrangement comprising: occupant position sensing meansfor obtaining a first approximation of the position of the occupant; andconfirmatory position sensing means for obtaining a second approximationof the position of the occupant when the occupant is wearing theseatbelt such that the position of the occupant is reliably determinablefrom the first and second approximations, said confirmatory positionsensing means being arranged to measure the length of the seatbeltpulled out of the seatbelt retractor.
 52. A method for determining theposition of an occupant of a vehicle situated on a seat in the vehicleand wearing a seatbelt, comprising the steps of: determining theposition of the seat or a part thereof relative to a fixed point ofreference; obtaining a first approximation of the position of theoccupant from the determined position of the seat or part thereof;measuring the length of the seatbelt pulled out of a seatbelt retractorassociated with the seat; and utilizing the measured length of seatbeltpulled out of the seatbelt retractor in combination with the firstapproximation of the position of the occupant to determine the positionof the occupant in the vehicle.
 53. A method for determining theposition of an occupant of a vehicle situated on a seat in the vehicle,comprising the. steps of: determining the position of the seat or a partthereof relative to a fixed point of reference; obtaining a firstapproximation of the position of the occupant from the determinedposition of the seat or part thereof; sensing the position of theoccupant of the seat to obtain a second approximation of the position ofthe occupant; and utilizing the second approximation of the position ofthe occupant in combination with the first approximation of the positionof the occupant to determine the position of the occupant in thevehicle; the step of sensing the position of the occupant comprising thestep of receiving waves from a space above the seat.